1. Field of the Invention
This invention relates to a graphite-crystal element used as a penetration radiation diffraction element.
2. Description of the Prior Art
It is well known that diffraction elements used for X-ray diffraction instruments such as an X-ray spectroscope, an X-ray microscope, etc. generally involve Bragg diffraction from a crystal. Crystals utilized for that purpose require that the crystal structure be complete, that crystals having the necessary size can be obtained, that the crystal have a absorption coefficient with respect to X-rays, and that the crystals are flexible when used for a crystal spectroscope or the like.
Graphite is one of materials which is desired as an X-ray diffraction element since the absorption coefficient relative to X-rays is low. CAPG (Compression-annealed pyrographite) marketed by Union Carbide Ltd. is obtained by annealing graphite crystal, under pressure, for a long period of time.
In the well known Bragg equation EQU 2d sin .theta.=.lambda.
d represents the spacing of a crystal lattice, .lambda. the wavelength of reflection X-ray, and .theta. the reflection angle. It is said in case of graphite of UNION CARBIDE LTD. that when a monochromatic X-ray, for example, K.alpha. line (.lambda.=1.5418 .ANG.) of Cu is reflected at the 002 face, the spacing d of the lattice is close to d=3.354 .ANG., which is the spacing of graphite monocrystal, and the width .DELTA..delta..sub.oo2 of the reflection line is approximately 0.7.degree.. However, when an attempt is made to obtain such graphite as described above, in the form of a monocrystal of natural graphite, it is impossible to obtain a monocrystal having a large area. If an attempt is made to obtain graphite by hot rolling a hot cracked sedimentary hydrocarbon material, annealing at high temperature for a long period of time under pressure is required, which involves a complicated manufacturing process, and results in high cost products.
In the past, flexed thin silicon monocrystal or graphite were machined to form a sphere. Such processes are cumbersome and costly.